The invention relates to a surface testing apparatus having a sensor holder and an apparatus whereby the sensor holder can be moved along a preselected path of movement over a surface to be tested.
In a known surface testing aparatus of this kind (DE-OS 33 24 444) there is provided a sensor holder which rotates on a circular path about a cylindrical test body. To assure a constant distance between the sensor holder and the surface being tested, a rotating drum bearing the sensor holder can be adjusted in two directions by means of a control system such that it is coaxial with the test body. Such control is effective only if the surface of the test body is actually cylindrical. But if the surface deviates from the cylindrical shape, an adjustment would have to be made at a plurality of points during each rotatioln of the drum, which for practical reasons is impossible at the desired high rotatory speed.
To avoid this disadvantage, the known apparatus has a sensor holder supported on the workpiece surface by an air system, so as to be able to compensate for local variations of the distance by means of the air pressure. Such an air system, however, is disadvantageous if the test bodies, for example, are steel slabs emerging from a continuous casting furnace, which, at time of the surface test, have a temperature of, e.g., 800.degree. to 1000.degree. C. and/or a rough surface. For the result would be that the pressure produced by the air system builds up only irregularly, and keeping the distance between test body and sensor holder constant with sufficient accuracy is impossible. Moreover, the known air system would make it impossible to provide additional control by means of the additionally present control system. Lastly, a similar use of the known surface test apparatus on test bodies having other, substantially flat surfaces, such as flat slabs, would not be very effective, since only the average distance between the sensor holder and the surface could be kept constant by means of the control system, and the remaining maximum deviations from this average would be too great. This applies quite plainly to test bodies such as flat steel slabs having a wavy surface whose contour can vary gradually.
It is, therefore, an object of this invention to improve the surface test apparatus of the kind specified such that no direct spacing regulation of the sensor holder will be necessary.
A further object is to design the surface test apparatus such that hot, rough surfaces will be able to be tested without problems.
Yet another object this invention is to provide an auxiliary supporting surface whose shape is closely adapted to the contour of the surface being tested and which has a preselected distance from the surface being tested.